Tetrahedron Letters 50 (2009) 5080–5082
Tetrahedron Letters
Hexachloroethane: a highly efficient reagent for the synthesis
of chlorosilanes from hydrosilanes
Veerachai Pongkittiphan a,b,c, Emmanuel A. Theodorakis c, Warinthorn Chavasiri a,b,
*
a Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand
b Center for Petroleum, Petrochemicals, and Advance Materials, Chulalongkorn University, Bangkok 10330, Thailand
c Department of Chemistry & Biochemistry, University of California, San Diego, La Jolla, CA 92093-0358, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 15 March 2009
Revised 9 May 2009
Accepted 22 May 2009
Available online 27 May 2009
A new and efficient chlorination protocol is presented for the preparation of chlorosilanes from hydrosil-
anes. A variety of chlorinating agents in combination with palladium(II) chloride as the catalyst are exam-
ined. Among them, hexachloroethane is found to be the best choice, furnishing the desired product in
good to quantitative yields under mild conditions. Various hydrosilanes are used as starting materials
to explore the scope of this reaction.
Ó 2009 Published by Elsevier Ltd.
Keywords:
Hexachloroethane
Hydrosilanes
Chlorosilanes
Palladium(II) chloride
Chlorinating agents
Chlorosilanes play an important role in organic synthesis for the
protection of highly reactive hydroxy and amino functional groups,
as reagents for Mukaiyama aldol condensations,1–4 or as precursors
of organochlorosilanes.5,6 In general, chlorosilanes are prepared by
treatment of hydrosilanes with alkyl or allyl chlorides in the pres-
ence of CuCl2,7 NiCl2, PdCl28,9 or Pd/C10 as catalysts. However, these
methods have certain limitations arising from the need for high
temperatures, long reaction times or the use of expensive and toxic
chlorinating agents.5,11 Recently, efficient systems were introduced
for the conversion of alcohols into alkyl chlorides using the combi-
nation of PPh3 and chlorinating agents such as Cl3CCOCCl3, Cl3CCN,
Cl3CCOOEt and Cl3CCONH2.12,13 Herein, we report a new and effi-
cient procedure for the preparation of chlorosilanes from hydrosil-
anes using chlorinating agents in the presence of a catalytic
amount of PdCl2.
Several chlorinating agents were explored for the conversion of
triisopropylhydrosilane (TIPS-H) into triisopropylsilyl chloride
(TIPS-Cl) (Table 1). The yields of TIPS-Cl were quantified by 1H
NMR spectroscopy using toluene as an internal standard.
As shown in Table 1 (entry 1), PdCl2 can transfer its chlorine
atoms quantitatively to TIPS-H. However, the use of hexachloroac-
etone, trichloroacetonitrile and trichloroacetamide in combination
with this catalyst produced TIPS-Cl in poor yields only (entries 3, 8
and 9, respectively). Of the three ethyl chloroacetates (entries 4, 6
and 7), Cl2CHCOOEt provided the highest yield of TIPS-Cl, while
Cl3CCOOEt, which has more chlorine atoms, gave a lower silyl chlo-
rination yield. Comparison of the chloromethanes (entries 13–15)
showed that CHCl3 furnished a higher yield of chlorination product
compared to CCl4 or CH2Cl2. The product yield can be increased by
carrying out these reactions at 55 °C for 3 h and 6 h, respectively
(entries 3 and 4). The more reactive acetyl chloride afforded
TIPS-Cl in quantitative yield (entry 2), however, due to its toxicity
and acidity, it cannot be used in certain cases. On the other hand,
comparison of different chloroethanes (entries 10–12) indicated
that hexachloroethane afforded the highest yield of TIPS-Cl. In fact,
0.5 M equiv of this reagent led to quantitative conversion of TIPS-H
into TIPS-Cl after only 1 h at 25 °C. When this reaction was re-
peated on a large scale, we were able to obtain a 99% yield of
TIPS-Cl after vacuum distillation (98 °C, 20 mmHg).14
Table 2 reveals the effect of the amount and type of catalyst
(PdCl2 or Pd/C) on this reaction. As expected, no reaction occurred
when the Pd catalyst was not present demonstrating that the cat-
alyst is essential (entry 1). Moreover, the product yield was
reduced to 81% when 0.5 mol % PdCl2 was employed (entry 3).
The results of the optimization studies on the amount of
Cl3CCCl3 required for this chlorination procedure are shown in
Table 3. Use of 0.17 M equiv of this reagent (corresponding to
1 equiv of chlorine atoms) under standard reaction conditions pro-
duced only a 69% yield of TIPS-Cl (entry 2). The yield of TIPS-Cl was
increased to 95% by using Cl3CCCl3 (0.30 mmol) (1.8 equiv of chlo-
rine atoms). The use of 0.5 mmol of hexachloroethane (3 equiv of
chlorine atoms) resulted in a quantitative yield of TIPS-Cl after only
30 min at room temperature (entry 5).
* Corresponding author. Tel.: +66 2 218 7625; fax: +66 2 218 7598.
0040-4039/$ - see front matter Ó 2009 Published by Elsevier Ltd.
doi:10.1016/j.tetlet.2009.05.087